Though he was related to Italian nobility, Philip came from a poor family. His father, Francisco Neri, worked as a notary. Philip’s brother died in childhood, but his two sisters, Caterina and Elisabetta survived. Known as a pius youth, Philip was taught humanities by the Dominicans.

The family moved to San Germano in 1533 to help some relatives with their business, and while there Philip would escape to a local Dominicanchapel in the mountains. Having received a vision that he had an apostolate in Rome, Philip cut himself off from his family, and went there.

With Persiano Rose, he founded the Confraternity of the Most Holy Trinity. He began to preach, with many converts. In 1550 he considered retiring to the life of a solitary hermit, but received further visions that told him his mission was in Rome. Later he considered missionary work in India, but further visions convinced him to stay in Rome.

He entered the priesthood in 1551. Father Philip heard confessions by the hour, could tell penitents their sins before they confessed, and had the gift of conferring visions. He began working with youth, finding safe places for them to play, becoming involved in their lives.